work from weekend

blackmesa/core/admin.py

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+from django.contrib import admin
+
+# Register your models here.

blackmesa/core/apps.py

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+from django.apps import AppConfig
+
+
+class CoreConfig(AppConfig):
+    name = 'core'

blackmesa/core/entities.py

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+from dataclasses import dataclass
+
+@dataclass
+class Planet:
+    name: str
+    weight: float
+    size: float
+    moons: int
+

blackmesa/core/migrations/0001_initial.py

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+# Generated by Django 2.2.17 on 2021-05-22 10:56
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Celestial',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=100)),
+                ('size', models.FloatField()),
+                ('weight', models.FloatField()),
+            ],
+        ),
+        migrations.CreateModel(
+            name='Orbit',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('distance', models.FloatField()),
+                ('celestial', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='orbits', to='core.Celestial')),
+                ('parent', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='children', to='core.Celestial')),
+            ],
+        ),
+    ]

blackmesa/core/models.py

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+from django.db import models
+from .workbench import PureManager
+
+# Create your models here.
+
+
+class Celestial(models.Model):
+    name = models.CharField(max_length=100)
+    size = models.FloatField()
+    weight = models.FloatField()
+    
+    objects = PureManager()
+
+class Orbit(models.Model):
+    parent = models.ForeignKey(Celestial, related_name='children', on_delete=models.CASCADE)
+    celestial = models.ForeignKey(Celestial, related_name='orbits', on_delete=models.CASCADE)
+    distance = models.FloatField()
+    
+    objects = PureManager()

blackmesa/core/tests/factories.py

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+from .. import models
+import factory
+import factory.fuzzy
+
+class CelestialFactory(factory.django.DjangoModelFactory):
+    name = factory.Faker('city')
+    weight = factory.fuzzy.FuzzyFloat(100.0, 100000.0)
+    size = factory.fuzzy.FuzzyFloat(1.0, 8.0)
+    
+    class Meta:
+        model = models.Celestial
+
+class OrbitFactory(factory.DjangoModelFactory):
+    parent = factory.SubFactory(CelestialFactory)
+    celestial = factory.SubFactory(CelestialFactory)
+    distance = factory.fuzzy.FuzzyFloat(2.0, 140.0)
+
+    class Meta:
+        model = models.Orbit

blackmesa/core/tests/test_base.py

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+from dataclasses import dataclass
+from django.test import TestCase
+from ..models import Celestial, Orbit
+from ..workbench import Lambda, PureDict
+from .factories import CelestialFactory, OrbitFactory
+from django.db.models.expressions import Expression, Combinable, Value
+from django.db.models import F
+from django.utils import functional
+# Create your tests here.
+
+
+class TestBase(TestCase):
+    def setUp(self):
+        TestCase.setUp(self)
+        self.celestials = CelestialFactory.create_batch(10)
+        self.orbits = []
+        for celestial in self.celestials[1:]:
+            self.orbits.append(OrbitFactory(parent=self.celestials[0], celestial=celestial))
+    
+    def test_data(self):
+        self.assertEqual(Celestial.objects.all().count(), len(self.celestials))
+        self.assertEqual(Orbit.objects.all().count(), len(self.orbits))
+    
+    def test_building_blocks(self):
+        klass = dict
+        queryset = Celestial.objects.purify(PureDict(), hi=Lambda(lambda x:'hi'))
+        data = queryset[0]
+        self.assertIsInstance(data, klass)
+        self.assertEqual(data['hi'], 'hi')
+    
+    def test_dataclass(self):
+        
+        @dataclass
+        class MyDataclass:
+            id: int
+            name: str
+            hi: str
+            size: float
+            weight: float
+        
+        klass = MyDataclass
+        queryset = Celestial.objects.purify(klass, hi=Lambda(lambda x:'hi'))
+        data = queryset[3]
+        self.assertIsInstance(data, klass)
+        self.assertEqual(data.hi, 'hi')
+        first = Celestial.objects.purify(klass, hi=F('name')).first()
+        self.assertIsInstance(first, klass)
+        self.assertEqual(first.hi, first.name)
+    

blackmesa/core/views.py

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+from django.shortcuts import render
+
+# Create your views here.

blackmesa/core/workbench.py

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+from django.db.models import QuerySet
+from django.db.models.expressions import BaseExpression, Combinable
+from django.db.models.query import ValuesIterable
+from django.db.models.manager import Manager
+
+"""
+
+    Base Idea:
+        - to have a queryset function that easily allows you to build some sort of "pure class" in a queryset.
+        - make it able to seamlessly use annotation functions
+        - allow callback modication of data, which is needed if your dataclass is frozen.
+    
+    By default the PureManager and PureQuerySet will use PureDataclass as handler, expecting your pureclass to be a dataclasses.dataclass type.
+    
+    An Example:
+    @dataclass
+    class MyClass
+        id: int
+        some_relation: str
+        next_id: int
+    
+    SomeModel.objects.filter(...).exclude(...).purify(MyClass, some_relation=F('some__model__relation'), next_id=Lambda(lambda x: x.get('id')+1))
+    
+    This allows you to move an iterator into another layer, where it either can be consumed, or used as an input for another queryset call,
+    but still guaranteeing, that regular usage of the iterator will not yield any smart object.
+    It is good if you want to build a best-of-both-worlds approach for subquery-capable repository pattern, which is one of the biggest issues if you want
+    to keep your business logic out of the repo layer, but still want to utilize djangos queryset mechanics properly.
+    
+"""
+
+## Useful for queryset function purify()
+class BaseLeap:
+    skip = False # if skip is true, this leap will not be actually processed.
+    resolves_field = True # if resolves_field is true, this leap will be called for a single field with resolve()
+    post_processing = False # if post_processing is true, this leap will in the end be called with dbdata, and be able to manipulate the whole dictionary.
+
+    def resolve(self, model, dbdata):
+        raise NotImplementedError
+
+    def post_process(self, model, dbdata):
+        raise NotImplementedError
+
+class Leap(BaseLeap):
+    """ value function that leaps SQL handling. """
+    def __init__(self, value=None):
+        self.value = value
+
+    def resolve(self, model, dbdata):
+        return self.value
+
+class Lambda(Leap):
+    """ leap value that calls a lambda expression. """
+    def __init__(self, callback):
+        self.callback = callback if callable(callback) else None
+
+    def resolve(self, model, dbdata):
+        # at this point i could check if callback needs 0-2 arguments and decide the call. 
+        if self.callback:
+            return self.callback(dbdata)
+        
+class Skip(BaseLeap):
+    """ Skips this key from being retrieved from the database or used in the dataclass instantiation """
+    skip = True
+    resolves_field = False
+
+class Callback(BaseLeap):
+    resolves_field = False
+    post_processing = True
+    def __init__(self, callback):
+        self.callback = callback
+    def post_process(self, model, dbdata):
+        if self.callback:
+            return self.callback(dbdata)
+
+## Wrapper to handle some sort of pure baseclass
+class PureHandler:
+    """ handler for a pure baseclass 
+    
+        defines how a pureclass can be created, and how to retrieve all field names, and the required ones.
+    """
+
+    @classmethod
+    def wrap(cls, klass):
+        return cls(klass)
+
+    def __init__(self, klass):
+        self.klass = klass
+
+    def create(self, **kwargs):
+        return self.klass(**kwargs)
+
+    def get_field_names(self):
+        return self.klass.__dict__.keys()
+
+    @property
+    def pureclass(self):
+        return self.klass
+
+    @property
+    def required_keys(self):
+        return self.get_field_names()
+
+
+class PureDict(PureHandler):
+    """ PureHandler that outputs a dictionary """
+
+    def __init__(self, klass=None):
+        # it is not required to define dict, but you could do OrderedDict e.g.
+        self.klass = klass or dict
+
+    def get_field_names(self):
+        # dictionary has no required fields.
+        return []
+
+
+class PureDataclass(PureHandler):
+    """ handles dataclasses.dataclass derivatives """
+
+    def create(self, **kwargs):
+        # clean field names to be only valid if they are on the dataclass.
+        pure_fields = self.get_field_names()
+        kwargs = {k: v for k, v in kwargs.items() if k in pure_fields}
+        return self.klass(**kwargs)
+
+    def get_field_names(self):
+        return list(self.klass.__dataclass_fields__.keys())
+
+# @TODO: PurePydantic
+
+###### QuerySet Plugin.
+
+class PureIterable(ValuesIterable):
+    """
+    Iterable returned by purify() that yields a pure class for each row.
+    Replaces the standard iterable of the queryset.
+    """
+
+    def __iter__(self):
+        queryset = self.queryset
+        model = self.queryset.model
+        query = queryset.query
+        compiler = query.get_compiler(queryset.db)
+        pure_data = getattr(queryset, '_pureclass_extra', {})
+        pure_handler = queryset._pureclass
+
+        # extra(select=...) cols are always at the start of the row.
+        names = [
+            *query.extra_select,
+            *query.values_select,
+            *query.annotation_select,
+        ]
+        indexes = range(len(names))
+
+        for row in compiler.results_iter(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size):
+            dbdata = {names[i]: row[i] for i in indexes}
+            # post-processors will be able to rewrite the whole dictionary.
+            post_processors = []
+            # we overwrite db data bluntly for now. actually we would provide callbacks the current dict.
+            for k, v in pure_data.items():
+                if v.resolves_field:
+                    dbdata[k] = v.resolve(model, dbdata)
+                if v.post_processing:
+                    post_processors.append(v)
+            if post_processors:
+                for processor in post_processors:
+                    processed = processor.post_process(model, dbdata)
+                    if processed is not None:
+                        dbdata = processed
+            yield pure_handler.create(**dbdata)
+
+
+class PureQuerySetMixin:
+    _pureclass_handler = PureDataclass
+
+    def purify(self, *args, **kwargs):
+        """
+            generates pure objects
+        
+            Acts like values(), however:
+                - first argument is a pureclass or purehandler, if not a string.
+                - if pureclass is not defined in purify, you have to define it on the queryset, or the model, with _pureclass,
+                  otherwise it will raise a RuntimeError.
+                - keyword arguments of type "Leap" are used as deferred values, and resolved independently.
+                - values() is called with every required_key on the dataclass not handled by a Leap
+        """
+        if len(args) and not isinstance(args[0], str):
+            # we assume this is our dataclass
+            # @TODO better checks.
+            handler = args[0]
+            args = args[1:]
+        else:
+            # determine dataclass.
+            handler = getattr(self, '_pureclass', getattr(self.model, '_pureclass', None))
+            if not handler:
+                raise RuntimeError("Trying to purify a class without destination class.")
+
+        if not isinstance(handler, PureHandler):
+            handler = self._pureclass_handler.wrap(handler)
+
+        all_keys = [*args, *kwargs.keys()]
+        unhandled_keys = list(set(handler.required_keys) - set(all_keys))
+        args = [*args, *unhandled_keys]
+
+        new_kw = {}
+        extra = {}
+        for k, v in kwargs.items():
+            if isinstance(v, Leap):
+                if not v.skip:
+                    extra[k] = v
+            elif isinstance(v, BaseExpression) or isinstance(v, Combinable):
+                new_kw[k] = v
+            else:
+                new_kw[k] = v
+
+        # copy ourself with values() and save the results on the cloned queryset.
+        values = self.values(*args, **new_kw)
+        values._iterable_class = PureIterable
+        values._pureclass_extra = extra
+        values._pureclass = handler
+        return values
+
+
+class PureQuerySet(PureQuerySetMixin, QuerySet):
+    # overwrite cloning.
+    def _clone(self):
+        c = super()._clone()
+        for key in ['_pureclass', '_pureclass_extra', '_pureclass_handler']:
+            if hasattr(self, key):
+                setattr(c, key, getattr(self, key))
+        return c
+
+# i use a mixin instead for better clarity. purify is completely safe, as it does not call _chain.
+# however you can also simply do:
+#class PureManager(BaseManager.from_queryset(PureQuerySet)):
+#    pass
+
+
+class PureManager(PureQuerySetMixin, Manager):
+    def get_queryset(self):
+        return PureQuerySet(self.model, using=self._db)